Sizzling summer not hot proof of global warming, scientists say

July 28, 1999
Web posted at: 8:47 p.m. EDT (0047 GMT)

(CNN) -- In the United States, sizzling temperatures are blamed for dozens of deaths; Russians suffer from the longest heat wave on record; Beijing sees its highest recorded temperature in a half-century.

The anecdotal evidence is hot enough to suggest that a larger phenomenon -- global warming -- might be to blame for the miseries of the summer of 1999. But scientists say that is a conclusion they are not prepared to make.

"A heat wave is a heat wave. We've always had them in the summer months, and they don't necessarily tell us anything about climate change," says Jim St. John, a meteorological scientist with the Georgia Institute of Technology in Atlanta.

Indeed, while there is a consensus among most scientists that human activity, such as burning fossil fuels, is having an effect on our climate, none of them is willing to say that the current heat wave, or any other, can serve as evidence of global warming.

Rather, they say temperature changes need to be traced over dozens or even hundreds of years to document trends.

"Chief evidence for global warming has been the running of long-range climate models and studying the history of temperatures over the last 100 years," St. John says. "It appears temperatures have increased about a half (degree) to a degree (Celsius) over the past 100 years."

Despite 1999's summer sizzle, the year has actually been somewhat cooler than previous years. If current trends hold, 1999 will be the first year since the early 1990s that a new record for global average temperatures will not be set.

However, 1999 is still likely to be the 23rd year in a row that global temperatures are above the long-term average.

The burning of fossil fuels may be a cause of global warming, scientists say

Blanketing heat

Supporters of the theory of global warming say that a huge increase in the amount of carbon dioxide and other gases, produced by burning fossil fuels, acts like a blanket, trapping heat close to the Earth's surface and raising temperatures.

The most authoritative report on global warming was issued in 1995 by the Intergovernmental Panel on Climate Change (IPCC), which drew on the work of 2,500 scientists.

The IPCC report concluded that global surface temperatures would rise by 1.4 to 6.3 degrees Fahrenheit (0.8 to 3.5 degrees Celsius) by the end of the next century. Melting polar ice and thermal expansion of ocean waters would cause the sea level to rise between 5 to 37 inches (13 to 94 centimeters) by 2100.

These changes could cause strong and more frequent storms and droughts, spur changes in agriculture, imperil many plant and animal species and inundate many coastal communities, the report concluded.

However, Tim Wigley, a U.S. government scientist who was a lead author of the report, said in June that IPCC's estimates might be low. He predicted temperatures will actually be a degree higher than the IPCC's calculations and that the rise in sea level will be two inches more.

However, other scientists dissent from the global warming hypothesis. They point out that the Earth has been slowly heating up since the days of Christopher Columbus -- long before cars or factories could have had any impact on climate.

An international treaty adopted in 1997 in Kyoto, Japan, called for the world's industrialized nations to set a timetable for reducing so-called "greenhouse" gases. But the United States, the world's current leader in greenhouse gas emissions, has not ratified the treaty, and many observers doubt it will be effective without American support.